Retroviral vector particles are useful agents for introducing polynucleotides into cells, such as eukaryotic cells. The term “introducing” as used herein encompasses a variety of methods of transferring polynucleotides into a cell, such methods including transformation, transduction, transfection, and transinfection.
Retroviruses typically have three common open reading frames, gag, pol, and env, which encode the structural proteins, encode enzymes including reverse transcriptase, and encode envelope proteins, respectively. Typically, retroviral vector particles are produced by packaging cell lines that provide the necessary gag, pol, and env gene products in trans. (Miller, et al., Human Gene Therapy, Vol. 1, pgs. 5-14 (1990)). This approach results in the production of retroviral vector particles which transduce mammalian cells, but are incapable of further replication after they have integrated into the genome of the cell.
Thus, retroviral vector particles have been used for introducing polynucleotides into cells for gene therapy purposes. In one approach, cells are obtained from a patient, and retroviral vector particles are used to introduce a desired polynucleotide into the cells, and such modified cells are returned to the patient with the engineered cells for a therapeutic purpose. In another approach, retroviral vector particles may be administered to the patient in vivo, whereby the retroviral vector particles transduce cells of the patient in vivo.
While the initial applications of human gene therapy have been performed in accessible sites and in target cells that are manipulated readily ex vivo, it is anticipated that future gene therapy protocols will describe systemic delivery of recombinant vectors for a wide variety of cardiovascular and other diseases. (Ledley, et al., Molecular Genetics and Gene Therapy of Cardiovascular Disease, Mockrin, ed., Marcel Dekker, Inc., New York, pgs. 467-485 (1995); Nabel, Circulation, Vol. 91, pgs. 541-548 (1995)). Development of the technologies associated with tissue targeting will expand greatly the scope of gene therapy in cardiovascular and other fields of medicine. The effectiveness of retroviral vectors for gene delivery to cardiovascular and other tissues is limited by the inefficiency of gene transfer into intact vascular endothelium, the inactivation of retroviral vectors in vivo, and by the inability to localize effective vector concentrations at remote physiological sites. Thus, the use of retroviral vectors in vivo for gene delivery to cardiovascular and other tissues depends upon effective viral titer, stability, tissue targeting, and the ability to transduce vascular cells. Presently, the targeted delivery of the therapeutic genes to impaired, diseased, or transplanted vasculature remains a major challenge in the development of gene therapy protocols for cardiovascular disease.